Feel simulators for aircraft



May 20, 1958 R. WESTBURY ETAL FEEL SIMULATORSQFOR AIRCRAFT Filed Nov. 29, 1955 M, 0m, M" flffa/z/z/fyaa United States Patent FEEL SIMULATORS FOR AIRCRAFT Roy Westbury, Bridgnorth, Solop, England, and Charles Philip Smith, Ramsey, Isle of Man, assignors to H. M. Hobson Limited, London, England, a British company Application November 29, 1955, Serial No. 549,764

Claims priority, application Great Britain December 7, 1954 3 Claims. (Cl. 244-83) This invention relates to hydraulic feel simulators for aircraft, fitted with power-operated control surfaces or in which the control surfaces are operated by servo tabs, of the kind, described in United States Patent No. 2,783,006, comprising a hydraulic jack coupled to the pilots control member and arranged to produce a resistance to movement thereof determined by the hydraulic control pressure prevailing in the jack, a pump for supplying liquid under pressure to the jack, a control valve movable from a neutral position to place the jack alternatively into communication with the pump and with exhaust and so varying the control pressure in the jack, and a device responsive to airspeed for actuating the control valve so as to increase or decrease control pressure in the jack in response, respectively, to increase or decrease in the airspeed.

In such an arrangement failure of the pump may be mitigated by the provision of a hydraulic accumulator. When, however, the pump fails the accumulator piston will in time reach the limit of its travel, so causing an abrupt loss of pressure in the jack. As will be understood, the pressure in the jack will fail when the main supply is cut off due to leakage and utilization of liquid by the pilot. If at this time the pilot is executing a manoeuvre involving pressure on his control member, he will inevitably move the control member to an excessive and sometimes disastrous extent.

The object of the present invention is to provide means whereby, in the event of failure of the main pressure supply, the control pressure in the jack can be gradually let down, over a period of say 5 to seconds, from a pressure providing normal feel to one providing low speed feel. This will give time for the pilot to adjust himself to the changed conditions and reduce considerably the risk of his moving his control member to an undesirable extent.

The invention accordingly provides a hydraulic feel simulator of the above kind comprising a spring loaded pressure accumulator connected to the conduit by which pressure liquid is supplied to the control valve downstream of a non-return valve in said conduit, said accumulator being normally held inactive by the pressure from the pump but serving, in the event of failure of the main pressure supply and consequent closure of the non-return valve, to supply liquid under gradually diminishing pressure to the jack through the control valve.

The piston of the accumulator is preferably loaded by a mechanical spring, although it may be loaded pneumatically if desired, and is normally forced back against the spring or air pressure by the pressure of the liquid. When, however, the main supply pressure fails the accumulator piston will be forced forward, by the spring or compressed air, to maintain, until such time as the accumulator piston has reached the end of its travel, a progressively diminishing control pressure to the jack.

One embodiment of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which:

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Fig. 1 is a diagram showing a typical installation according to the invention, and

Fig. 2 is a longitudinal section through the control unit and associated pressure accumulator.

As indicated in Fig. 1, a pilots control member 10, pivoted at 11, is connected by a member 9 to the transmitter 12 of a servo mechanism for actuating the control surface 13 of an aircraft. The receiver of the servo mechanism is shown at 14, and the servo mechanism 12, 14 serves in the well known manner to displace the control surface 13 in a direction and to an extent determined by the movement imparted to the control member 10.

The feel simulator comprises a hydraulic jack 15 and an associated control unit 16. The cylinder 17 of the jack is pivoted at 18 to a fixed anchorage and the piston 19 of the jack is connected to the control member 10, as indicated, through the agency of a lever 20 pivoted intermediately at 21 to a fixed anchorage. The feel imposed by the jack 15 on the control member 10 is determined by the hydraulic control pressure prevailing in the jack 15 and transmitted thereto by a signal line 22 from the control unit 16.

Hydraulic pressure is supplied to the control unit 16 by a hydraulic pump 23 through a pressure supply line 24 containing a non-return valve 25. The pump 23 draws liquid from a reservoir 26, to which liquid is returned from the control unit 16 and from the jack 15 by exhaust lines 27, 28 respectively.

As indicated in Fig. 2, the control unit 16 has an inlet 29 communicating with the pressure line 24, an outlet 30 communicating with the signal line 22 and an exhaust outlet 31 communicating with the exhaust line 27. Mounted in the control unit is a piston-type control valve 32 having lower and upper lands 53, 54 for respectively controlling.communication between the outlet 30 and inlet and exhaust ports 33, 34. The undersurface of the control valve 32 is subject, through a duct 35 and the outlet 30, to the pressure prevailing in the signal line 22,i. e. to the control pressure prevailing in the jack 15 (Fig. l). The control valve is normally held balanced against the control pressure, in the position indicated in Fig. 2, by the downward pressure exerted on it by a diaphragm 36 through the agency of a push rod 37, assisted by the pressure of a spring 38.

Ram pressure is applied to the upper surface of the diaphragm 36 through an inlet 43 and static air pressure is supplied to the undersurface of the diaphragm through an inlet 44. On increase in the airspeed the diaphragm moves the control valve 32 downwardly, connecting the outlet 30 to the pressure port 33, so admitting liquid under pressure to the jack 15. The control valve 32 is moved back to the neutral position shown by the increased control pressure beneath it as soon as the control pressure in the jack has built up to the level determined by the diaphragm. On decrease in the airspeed, the downward force on the diaphragm 36 is reduced, the control valve 32 is moved upwardly to connect the outlet 30 to the exhaust port 34, so allowing liquid to flow from the jack 15 to exhaust until the control pressure in the jack has fallen to a value determined by the reduced loading on the diaphragm.

At low airspeeds, a spring 39 holds the diaphragm 36 out of contact with the push rod 37 and the control pressure in the jack is then determined solely by the loading of the spring 38. A relief valve 46 is disposed between the control valve and the push rod, the control pressure acting on the undersurface of the relief valve through a passage 41. The relief valve is normally held on its seat by the push rod 37, assisted by the pressure of the spring 38. If, however, the control pressure should become excessive, as the result of seizure of the control valve 32,

the relief valve 40 will lift and allow liquid to flow from the jack to exhaust through a.passage 42.

Connected to the pressure supply conduit to the control valve, at a point downstream of the non-return valve 25, is a small capacity pressure accumulator 45, consisting of a cylinder 46, containing a piston 47 ,loadedby a spring 48. As shown in Fig. 2, the accumulator can conveniently be built into the control unit 16, the cylinder 46 being fitted alongside the boss accommodating the control valve and communicating by a duct 49 with the inlet port 33 and the non-return valve 25 being included in the pressure inlet 29 to the control unit. The accumulator serves, as already described, to provide an emergency supply of pressure liquid to the control valve in the event of failure of the main pressure supply.

Although we make no claim to this feature, we prefer to provide, as shown in Fig. 1, a relief valve 50 in a bypass line 51 connecting the signal line 22 and the exhaust line 28, the valve 50 being normally held closed, as shown,

by the pressure of the main supply (when available) or of the accumulator. Without such a relief valve, when the control member is moved after the pressure supply from the accumulator has ceased, liquid can only be expelled from the jack in small quantities at a time through the control valve. velop in the cylinder of the jack and there will be an undesirable, sudden increase in resistance to movement of the control member when the control member has been moved sufliciently for the jack piston to reach the limit of the dead space. This is eliminated by the provision of the relief valve 50, which can open, as soon as the accumulator 45 has run down, to allow liquid to flow freely from the jack to exhaust.

What we claim as our invention and desire to secure by Letters Patent is:

l. A feel simulator for an aircraft having a control surface actuable under power control by a pilots control member, said feel simulator comprising, in combination with said control member, a piston, a housing for the piston having an outlet, means connected to the control member and effective on movement thereof in either direction from a neutral position to cause relative movement of said piston and housing and thereby to expel liquid Consequently a dead space will dethrough said outlet, valve mechanism normally closing said outlet, inlet and exhaust ports controlled by said valve mechanism, said valve mechanism operating to connect said outlet to said exhaust port on movement of said control member, a pump, a conduit for supplying liquid under pressure from said pump to said inlet port, a non-return valve in said conduit, a spring loaded pressure accumulator connected to said conduit at a point downstream of the non-return valve and normally held charged by the fluid pressure in said conduit, and a device responsive to changes in airspeed arranged to actuate said valve mechanism to connect said outlet alternatively 4 to said inlet port and to said exhaust port in response respectively to increase and decrease in airspeed and thereby to establish in said housing a hydraulic pressure which increases with airspeed, said accumulator operating, on failure of pressure from said pump and on continued operation of said valve mechanism, to supply liquid to said housing under gradually diminishing pressure.

2. A feel simulator as claimed in claim 1, wherein said.

airspeed responsive device is a diaphragm situated in a casing and exposed at its opposite sides to ram pressure and to atmospheric pressure, and said valve mechanism is constituted by a piston valve in said casing subject at one end to pressure from said diaphragm and at the other end, through a signal line connecting the casing to the housing, to the fluid pressure in the housing, said casing having an inlet for transmitting fluid pressure from said conduit to said inlet port and said accumulator being disposed in said casing and communicating with said inlet port.

3. A feel simulator as claimed in claim 2, wherein said nonreturn valve is disposed in the casing and controls the passage of fluid from the inlet to the inlet port.

References Cited in the file of this patent UNITED STATES PATENTS Greenland et al Apr. 9, 

